G.f.: -x*(x-1)*(1+x)/(1-x-7*x^2-x^3+x^4).

Terms

a(0) =0a(1) =1a(2) =1a(3) =7a(4) =15a(5) =64a(6) =175a(7) =631a(8) =1905a(9) =6433a(10) =20224a(11) =66529a(12) =212625a(13) =692119a(14) =2226799a(15) =7217728a(16) =23284815a(17) =75343591a(18) =243328225a(19) =786800449a(20) =2542156800a(21) =8217744577a(22) =26556314401a(23) =85835882791a(24) =277405671375a(25) =896595420736